The present invention relates to a motor stator and a phase coil preform used for a motor stator and, more specifically, to a stator core of the motor stator having a plurality of teeth forming slots between any two adjacent teeth and plural phase coil formed by wave winding and provided in the slots.
In a motor, torque pulsation per rotation of a motor rotor is generated at the least common multiple of the respective numbers of the slots for coils and the poles of the motor. The larger the number of torque pulsations per rotation is, the smaller the amplitude of the torque pulsation is. Therefore, an increased number of slots is desired as disclosed in Japanese Application Publication 2009-33832.
Coils for the motor stator disclosed in the above Publication are formed by wave winding. Each phase coil, namely an U-phase coil, a V-phase coil or a W-phase coil is divided into two groups of coil. One group of slots through which first wave winding bundle of each phase coil is wound is separated from the other group of slots through which second wave winding bundle of the phase coil is wound. This arrangement is employed for increasing the number of slots. The number of slots in the case in which each phase coil is divided into two groups is twice as many as that in which each phase coil is not divided into two groups.
In providing the respective phase coils in the slots of the motor stator according to the above Publication, the two groups of each phase coil are passed through the slots independently and then connected each other by a connection wire. However, such connecting operation is time-consuming and laborious and furthermore the connections should be insulated appropriately by covering with insulating material.
The present invention is directed to providing a motor stator and a phase coil preform that dispense with the operation of connecting electrically a first wave winding bundle and a second wave winding bundle in fabrication process.